Temporarily revert r135528 which distinguishes between two copies of one

inlined variable, based on the discussion in PR10542.

This explodes the runtime of several passes down the pipeline due to
a large number of "copies" remaining live across a large function. This
only shows up with both debug and opt, but when it does it creates
a many-minute compile when self-hosting LLVM+Clang. There are several
other cases that show these types of regressions.

All of this is tracked in PR10542, and progress is being made on fixing
the issue. Once its addressed, the re-instated, but until then this
restores the performance for self-hosting and other opt+debug builds.

Devang, let me know if this causes any trouble, or impedes fixing it in
any way, and thanks for working on this!

llvm-svn: 136953